Varifocal objective with four-component front lens group



magsmaofa Dec. 30, 1969 KMAcHl-:R

VARIFOCAL OBJECTIVE WITH FOUR-COMPONENT FRONT LENS GROUP Filed March 2'7, 1967 rn r1.3 H5 r1? r19 r21 fzs f2s r 7 f2s Ira rzz f4 rz I r1 r3 r5 r r r2 r4 r6 f8 r0 rZ r4 rE r8 dz dza 17 d19 d21 d23| dl5dl6 dl8 d20 dZZ dZ d25 III 5' Karl Macher Inventor.

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United States Patent O 3,486,809 VARIFOCAL OBJECTIVE WITH FOUR-COM- PONENT FRONT LENS GROUP Karl Macher, Bad Kreuznach, Germany, assignor to Jos. Schneider & Co., Optische Werke Kreuznach, Bad Kreuznach, Germany, a corporation of Germany Filed Mar. 27, 1967, Ser. No. 626,172 Claims priority, application Germany, Apr. 5, 1966, Sch 38,786 Int. Cl. B29d 15/00 U.S. Cl. S50-184 10 Claims ABSTRACT OF THE DISCLOSURE Varifocal objective system with fixed-focus rear lens group and a four-component front lens group of variable focal length, the latter group being composed of a positive and axially fixed iirst component consisting of a dispersive front lens followed by three collective singlets, a negative and axially movable second component consisting of a dispersive singlet followed by a dispersive triplet with positively refracting cemented surfaces, a negative and axially movable third component consisting of a dispersive doublet with a negative and a positive lens separated by a negatively refracting cemented surface, and a positive and axially fixed fourth component consisting of two air-spaced collective singlets, the objective having a varifocal range of substantially :1 with a relative aperture of 2: 1.

The present invention relates to an improvement of a varifocal optical objective system for photographic or cinematographic cameras as disclosed in my pending U.S. application Ser. No. 295,851 liled July 17, 1963, now Patent No. 3,346,320.

The objective system disclosed in my earlier application is divided, in the usual manner, into a varifocal front attachment and a rear lens group constituting a basic or fixed-focus objective, the front attachment having two axially movable negative components bracketed by two substantially fixed positive components. The term substantially fixed allows for the possibility that one of these positive components, especially the one in front, be limitedly adjustable for focusing purposes, either in its en tirety or in some of its parts.

As further disclosed in my earlier application, the positive first component of the varifocal front group advan tageously consists of four air-spaced singlets including a dispersive front lens and three collective lenses following same, the separation between this front lens and the three following singlets being less than one-fourth of the individual focal length of this particular component; the movable second component, of negative refractivity, consists of two air-spaced dispersive lens members of which the first one is a singlet while the second one is a doublet. The movable negative third component is preferentially also designed as a doublet while the fourth component is a positive singlet. The fixed rear lens group of my earlier disclosure consists of four air-spaced lens members of which the first, second and fourth ones are positive singlets while the third one is a negative doublet.

The aforedescribed system, while operative with rela- I tive aperture of l:l.4, has a varifocal range (i.e. a ratio of its maximum and minimum overall focal length fmax and fmm) of only 6: 1, the individual focal length f1 of the ICC front component being substantially larger than fmax and amounting to approximately three times the median value of the varifocal range.

The principal object of my present improvement is to provide an objective system of the general type disclosed in my prior application but with a .considerably enlarged varifocal range of approximately 10:1, with maintenance of a relative aperture as high as 1:2.

A more particular object of this invention is to provide an improved objective system of the type described wherein, with fm1 smaller than the image diagonal, the frontlens diameter needs to be only slightly greater than that of the entrance pupil in the position of maximum overall focal length, with complete illumination of the image field even upon adjustment of the first component for focusing at short distances so as to avoid objectionable vignetting during close-ups.

In accordance with my present invention, the individual focal lengths fr, fn, fm, fw of the four components of the varifocal front group as well as the individual focal length jv of the fixed-focus rear group are so dimensioned that fw is less than of f1 and that the absolute value of fm exceeds by at least 10% the absolute value of fn, fr being less than 4 fv; furthermore, fv lies approximately at the center of the varifocal range fmaX-fmm, with the other individual focal lengths f1, fn, fm and fw having their absolute values preferably also included within that range. v

To help realize the aforedescribed relationship of the various individual focal lengths, the refractive powers of the second member of the axially movable second component are advantageously distributed over four optically effective surfaces, i.e. the two outer surfaces and the two cemented inner surfaces of a triplet, the cemented inner surfaces being positively refracting and preferably so curved that their combined power has an absolute value ranging betweenone-third and one-fifth of the absolute value of the combined power of the negatively refracting outer surfaces of the triplet. This triplet may have an overall biconcave configuration and its central lens may also be biconcave, each of its three consitituent lenses having a refractive index nd greater than 1.6, with the refractive indices of the meniscus-shaped outer lenses exceeding that of the central lens by less than 0.15. This relationship has been found to minimize particularly the transverse chromatic aberration.

vA similar distribution of powers can be provided, in accordance with still another feature of my invention, at the axially fixed fourth component by dividing the latter into two closely spaced positive singlets. This measure spreads the strongly collective effect of the fourth component and counteracts an undercorrection ofthe spherical aberration.

In order to realize the relatively large aperture ratio of 1:2 with a minimum of spherical zonal aberration, I prefer to construct the basic objective or rear lens group from four air-spaced lens members including three positive singlets and one negative doublet, as in the system of my earlier application above identified, yet with the difference that the negative doublet is to occupy the second position rather than the third one within the group. Good chromatic correction is obtained if the refractive indices constituted of this doublet, designed as a biconcave member, are greater than 1.65 and differ by more than 0.03 across the forwardly concave, positively refracting cemented surfaces thereof, yet with a difference of not more than iunits between the Abb members u of the constituents of the doublet; this arrangement reduces the curvature of the outer surfaces of the doublet and minimizes the Gaussian aberration.

The use of a doublet as the third component further reduces the chromatic aberation of the overall system. The adjustable front group of my improved system is strongly collective, with convergence of the light rays beyond its fourth component, at least near its lower end of the varifocal range so that the individual focal length fv of the rear length group may be larger than would otherwise be possible, with resulting attening of the curvatures of that group.

The invention will vbe described in greater detail with reference to the accompanying drawing in which:

FIG. 1 diagrammatically illustrates an embodiment of my invention; and

FIG. 2 is a graph showing the relative positions of the two movable components of the adjustable front group of the system of FIG. 1 throughout its varifocal range.

The objective system shown in FIG. l comprises four components I, II, III and IV, together constituting a varifocal front group, and a four-member rear group V representing a basic or principal objective from which the varifoeal group may be detached if desired. Cornponent I, which may be limitedly axially displaceable for focusing purposes but will otherwise be considered as fixed, consists of a dispersive front lens L1 with radii r1, r2 and thickness d1, a first positive singlet L2 (radii r3, r4 and thickness d3) separated from lens L1 by an air space d2 which is less than one-fourth of the individual focal length f1 of component I, a second positive singlet L3 (radii rS, r6 and thickness d5) separated from singlet L2 by an air space d4, and a third positive singlet IA (radii f7, r8 and thickness d7) separated from singlet L3 by an air space d6. A variable air space d8 Separates component I from the axially movable negative component II which consists of a forwardly convex meniscusshaped negative singlet L5 (radii r9, r10 and thickness d9) and, spaced from it by a distance d10, a biconcave triplet composed of a first meniscus-shaped outer lens L6 radii r11, r12 and thickness dll), a biconcave central lens L7 (radiir12, r13 and thickness :112) and a second meniscus-shaped outer lens L8 (radii r13, r14 and thickness 113). Another variable air space d14 intervenes between component II and the second axially movable negative component III which is in the form of a forwardly concave meniscus-shaped doublet `composed of a biconcave lens L9 (radii r15, r16 and thickness d15) cemented into a biconvex lens L (radii r16, r17 and thickness d16). A third variable air space d17 exists between component III and the axially fixed positive component IV which consists of two biconvex lenses L11 (radii r18, r19 and thickness 118) and L12 (radii r20, r21 and thickness d20) which are spaced apart a short distance d19. Following a further air space d21, there is disposed the rst lens member L13 of group V in the form of a concavoconvex positive singlet with radii r22,

r23 and thickness d22. Next, separated from lens L13 by an air space d23, there is a biconcave doublet whose constituent lenses are a positive meniscus L14 (radii r24, r25 and thickness d24) and a biconcave' lens L15 (radii r25, r26 and thickness d25). Separated from this doublet by an air space d26 is a biconvex lens L16 (radii 127, r28 and thickness d27), followed after an air space d28 by the last lens L17 in the form of a biconvex member of radii r29, r30 and thickness d29.

In the following Table A I have listed representative numerical values for the radii r1 to r30 and the thcknesses and separations d1 to d29 of lenses L1 to L17, base on a minimum overall focal length fmm of one linear unit (eg. 1 mm.), together with their refractive indices nd and Abb numbers v, given for a spectral wavelength A=587.6 ma (5876 A.), as well as the refractive powers An/r for each of the lens surfaces (to be compared with an overall power of unity): I

TABLE A.

Thlcknesses Radii and nd v A11/r separations rl=l0.28 0. 06086365 L1.-- d1=0.244 1. 71736 20. 51

d2=0.471 air space r3= +11.058 +0. 05792186 L2--. d3=0.9l0 1. 64050 r4= 11.058 +0. 05702186 I d4=0.008 air space r5= +32.114 +0. 01994457 L3.-- d5=0.581 1 64050 d6=0.008 air sp r7= +5358 +0 13307204 L4--. d7=0.589 1 71300 89 d8 0.046 air space (variable) r9= +4843 4268015 L5. d9=0.163 1 69100 7l d10=0.650 air space r11= 5.124 713895 II- L6..- d11=0.252 1 80518 25. 46V

r12= 2.911 +0. 03166609 L7 d12=0.163 1 71300 53. 89

r13= +2911 +0. 03166609 L8.-. dl3==0.3l7 1.80518 25. 4G

d14 =3.981 all' Space (variable) rl5= 2.307 -0. 29745515 L0. d15=0.163 1. 71300 53. 89 111 r16= +3.639 0. 00661445 Ll0 dl6=0.325 l. 68893 3l. 15

d17=1.371 air s pace (variable) T18 +12.202 +0. 04313227 L11- d18=0.285 1. 52630 5l. 00

r19= 4.853 0. 10844838 IV.. d19=0.008 air sp2 ce r20= +5233 +0. 09984521 L12. d20=0.244 1. 52249 59. 64

|121 =0.244 air space r22= +2003 +0. 24225162 L13-. d22=0.488 l. 48523 d23=0.325 air space r24 4.017 0. 16160208 L14- d24=0.772 1. 70504 r25= 1.395 +0. 03888172 L15 d25=0.167 1. 74080 V-.. r26= +1898 0. 39030558 d26=0.366 air space r27= +5.86? +0. 08270495 L16 127 =0.382 1. 48523 d28=0.045 air space r29=+2.525 +0. 19217029 L17. 129 =0.374 1. 48523 The objective system represented by the foregoing Table A has a relative aperture of 1:2, a minimum overall focal length fmm of one unit and a maximum overall focal length fum of nearly ten units. The variable air spaces d8, d14 and d17, given in the table for the starting position f=fm1m always add up to 5.398 as illustrated in FIG. 2 which shows the law of motion for the two negative components l1 and III. In addition, Table B below gives the numerical values of these variable air spaces for five distinct positions of components II and III:

TABLE B The individual focal lengths of components I, Il, III, IV and V are calculated as follows:

It will thus be seen that the value of fv lies close to the midpoint (f-5.5) of the varifocal range of the system.

It is to be understood that the values of Tables A and B are valid within tolerance limits of substantially i% for the radii r1 to r30, the thicknesses and separations d1 to d29, the surface powers An/r and the Abb numbers v and of substantially :0,02 for the refractive indices nd.

Iclaim:

1. In an optical objective system including a fixedfocus rear lens group, the combination therewith of a forward lens group consisting of a substantially fixed positive first component, an axially movable negative second component, an axially movable negative third component and a fixed positive fourth component; said first component including three air-spaced collective lens members and a dispersive front lens preceding said collective lens members, said front lens being air-spaced from the next one of said collective lens members by a distance less than substantially one-fourh of the individual focal length'fI of said first component; said second component consisting of two air-spaced dispersive lens members; said second and third components being displaceable between two extreme positions in which the overall focal length of the system assumes respective values imm and fmx defining the lower and upper limits of a varifocal range substantially centered on said individual focal length fvg said individual focal lengths having substantially the follow- 2. The combination defined in claim 1 wherein the ratio of fmx to imm substantially equals 10:1, the system having a relative aperture of 1:2.

3- The combination defined in claim 1 wherein the dispersive lens members of said second component are a forwardly convex meniscus-shaped singlet and, following same, a triplet with two positively refracting cemented surfaces.

4. The combination defined in claim 3 wherein said triplet is biconcave and composed of a biconcave central lens and two meniscus-sbaped outer lenses.

5. The combination defined in claim 1 wherein said third component is a forwardly concave meniscus-shaped doublet consisting of two oppositely refractive lenses separated by a forwardly convex and negatively refracting cemented surface.

6. The combination defined in claim 1 wherein said fourth component consists of two air-spaced biconvex singlets.

7. The combination defined in claim 1 wherein said rear lens group consists of a positive first lens member, a negative second lens member, a positive third lens member and a positive fourth lens member all air-spaced from one another.

8. The combination defined in claim 7 wherein the dispersive front lens and the collective lens members of said rst component are singlets, the dispersive lens members of said second component being a meniscus-shaped singlet and a triplet, said third component being a meniscus-shaped doublet consisting of two oppositely refractive lenses separated by a negatively refracting cemented surface, said fourth component consisting of two air-spaced collective singlets, the negative second lens member of said rear lens group being a biconcave doublet, said positive first, third and fourth lens members of said rear lens group being singlets.

9. The combination defined in claim 8 wherein said biconcave doublet is composed of two constituent lenses of opposite refractivity separated by a forwardly concave and positively refracting cemented surface.

10. The combination dened in claim 9 wherein the numerical values of the radii r1 to r30 and the thicknesses and separations d1 to d29 of said front lens L1, said three air-spaced collective lens members L2, L3, L4, said meniscus-shaped singlet L5, the constituents L6, L7, L8 of said triplet, said oppositely refractive lenses L9, L10 of said meniscus-shaped doublet, said two air-spaced collective singlets L11, L12, said first lens member L13, the constituent lenses L14, L15 of said second lens member, said third lens member L16 and said fourth lens member L17, based -upon an overall minimum focal length fmm of numerical value l, their refractive indices nd and their Abb numbers v, for a wavelength 1:5876 m/i, are substantially as given in the following table:

Tnlcknesses Rdll and n.1 v

separations r1= -10.268 L1 dl=0.244 1. 71736 29. 51

d2=0.471 air space r3= +1l.058 L2 d3=0.919 1. 64050 60, os

d4=0.008 air space r5=+32.114 L3 d5=0.581 1. 64050 60. 08

d8=0.008 air space r7=+5.358 L4 d7=0.589 1. 71300 53. 89

d8=0.046 air space (variable) r9=+4.843 L5 d9=0.163 1. 69100 64. 71

d10=0.650 air space rl1= 5.124 L6 dl1=0.252 1. 80518 25. 46

r12= -2.9l1 L7 d12=0.163 1. 71300 53. 89

r13= +2911 L8 dl3=0.317 1. 80518 25. 46

r14= +1o.02s

dl4=3.981 air space (variable) rl5= -2.397 L9.. dl5=0.l63 1. 71300 53. 89

r16= +3.639 L10 dl6=0.325 1. 68893 31. 15

d17= 1.371 air space (variable) rl8= l12.202 L11 dl8=0.285 1. 52630 51. 00

d19=0.008 air space r20= +5233 L12 d20=0.244 l. 52249 59. 64

r2l= +45.69l

d21=0.244 air space r22= +2003 L13 d22=0A88 l. 48523 8l. 61

r23= +2l.l54

d23=0.325 air space r24= -4.917 L14 d24=0.772 1. 79504 28. 39

T25 1.395 L15 d25=0.l67 1. 74080 28. 05

d26=0.366 aix space r27= +5.86? L16 d27=0.382 1. 48523 81. 61

d28=0.045 air space r29= +2525 L17 d29=0.374 1. 48523 81. 61

(References on following page) 7 1 8 References Cited DAVID SCHONBERG, Primary Examiner UNITED STATES PATENTS P. A. SACHER, Assistant Examiner 3,363,964 1/ 1968 Macher 350-176 Us. CL XR.

FOREIGN PATENTS 5 350-186 1,417,663 10/1965 France. 

